This application is based on application No. 021425 filed in Japan on Jan. 31, 2000, the content of which incorporated hereinto by reference.
This invention relates to a power supply apparatus to drive a hybrid car.
A hybrid car runs by driving wheels with an engine and an electric motor. A driving battery is installed as the power source to drive the electric motor. This driving battery is charged by a generator. The generator is driven by the engine or by regenerative braking which uses inertial force to drive the generator when the automobile is stopping. The amount of charge and discharge for the driving battery is controlled by a battery control circuit, and the remaining battery capacity is regulated within a specified range. This is because over-charging and over-discharging cause rapid degradation in the electrical characteristics of the driving battery. The battery control circuit, which controls charging and discharging of the driving battery is contained along with the driving battery within the battery system.
In this power supply apparatus, over-discharge of the driving battery will not occur as long as the automobile is operated under normal conditions. However, if the vehicle is not used for a long period, the driving battery may discharge and not be able to drive the electric motor. Since the electric motor which drives the wheels of a hybrid car serves a dual purpose as starter motor for the engine, the engine cannot be started if the driving battery is discharged.
This situation can be corrected by charging the driving battery from an external source. However, since the driving battery contains more than 1000 rechargeable batteries to attain a substantially high voltage, it is necessary to charge the driving battery with a special-purpose battery charger. Inability to drive the vehicle due to discharge of the driving battery is an extremely rare event. Therefore, it is impossible from a practical standpoint to provide a special-purpose battery charger to correct this rare event.
This dilemma can be solved by starting the engine with an automotive electrical system battery. However, since the output voltage of automotive electrical system batteries is almost without exception 12V, either a special starter motor must be used to start the engine, or an inverter is necessary to raise the voltage from 12V DC to the voltage of the electric driving motor. In providing a starter motor, it is necessary to equip the engine with a starter motor which is almost never used, and increase manufacturing cost. In providing an inverter, it is necessary to make, inverter output extremely high, and this also has the drawback of excessively high manufacturing cost.
The present invention was developed to resolve these types of problems. Thus it is a primary object of the present invention to provide a hybrid car power supply apparatus which can charge the driving battery with an automotive electrical system battery and a low cost system, and which can start the engine when the driving battery has been over-discharged.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The hybrid car power supply apparatus of the present invention is provided with a battery system, an inverter to supply power output from a driving battery inside the battery system to the electric motor, and an automotive battery used as power source for standard automobile electrical equipment. The battery system is provided with a driving battery for powering the vehicle driving motor and a battery control circuit to control charging and discharging of the driving battery. Further, the battery system contains a charging circuit for charging the driving battery with the automotive electrical system battery. When the remaining battery capacity of the driving battery drops below a set value, the charging circuit charges the driving battery with power from the automotive electrical system battery. The charged driving battery drives the electric motor to start the engine.
The hybrid car power supply apparatus described above has the characteristic that a low cost system allows the vehicle to be started when the driving battery has been over-discharged. This is because the battery system which houses the driving battery also contains a charging circuit. This charging circuit charges the driving battery via the automotive electrical system battery. Namely, the charging circuit within the battery system charges the driving battery with power from the automotive battery and the charged driving battery operates the electric motor to start the engine. This configuration has the characteristic that the charging circuit can be made at low cost and with high reliability. This is because the driving battery can be charged by the automotive battery over a given length of time. Therefore, charging circuit output current can be relatively small and still charge the driving battery to operate the electric motor.
When remaining driving battery capacity becomes low, the electric motor could alternatively be directly powered by the automotive battery to start the engine without relying on the system above. However, in this case, an extremely high output special-purpose inverter is required to drive the electric motor with the automotive battery. Since extremely high current must flow at the instant the electric motor is turned over, this inverter must be designed for high power output and becomes an expensive item.
However, the inverter provided in the hybrid car for running the electric motor via the driving battery can be used to avoid driving the electric motor directly with the automotive battery. This is possible by charging the driving battery with the automotive battery and running the electric motor via the driving battery. A charging circuit to charge the driving battery from the automotive battery is required, but it is not necessary to instantaneously charge the driving battery and the charging circuit can be a low current, low cost device. Further, since there is no high current flow over short periods, reliability is improved, operating life extended, and maintenance simplified.
This system has the characteristic that simply by connecting an automotive battery to the hybrid car, the driving battery can be charged and the engine started by the electric motor even when remaining battery capacity becomes low. This is because the battery system is equipped with a charging circuit to charge the driving battery via the automotive battery.
In this battery system, it is preferable to detect remaining battery capacity of the driving battery and the automotive battery via the battery control circuit. When remaining driving battery capacity drops below a specified level, and remaining automotive battery capacity is above a specified level, the automotive battery charges the driving battery.
In addition, the battery system charging circuit can also house a circuit to charge the automotive battery from the driving battery. In this battery system, the battery control circuit detects remaining battery capacity of the driving battery and automotive battery. When remaining driving battery capacity is above a specified level, and remaining automotive battery capacity is below a specified level, the driving battery charges the automotive battery.
Since the driving battery of this power supply apparatus can charge the automotive battery, power from the driving battery taken during forced discharge of the driving battery can be efficiently used to charge the automotive battery. The driving battery is actually many rechargeable batteries connected together. Therefore, the driving battery has the property that battery capacity differences between individual batteries become large through repeated charge-discharge cycles, upsetting the balance of battery capacities. If a driving battery having rechargeable batteries with unbalanced capacities is charged and discharged, some battery may over-charge or some battery may over-discharge. Further, to extend driving battery life as much as possible, shallow charging and discharging is repeatedly performed. As a result, depending on battery type, effective usable battery capacity can decrease due to the xe2x80x9cmemory effectxe2x80x9d. A driving battery in these conditions can be forcibly discharged to recover from battery capacity imbalance and xe2x80x9cmemory effectxe2x80x9d. At these times, if discharge power is used to charge the automotive battery, driving battery discharge is not wasted and the automotive battery can be efficiently charged.
Further, the battery system can be provided with a driving battery cooling fan powered by the automotive battery to avoid driving battery over-heating. Still further, the automotive battery can also be used as back-up power for the battery control circuit.